Conventionally, a microphone unit, which has a function to convert an input sound into an electric signal and output it, is applied to: voice communication apparatuses such as a mobile phone, a transceiver and the like; information process systems such as a voice identification system and the like that use a technology for analyzing an input voice; or recording apparatuses and the like, and various microphone units are developed (e.g., see patent documents 1 to 3).
Among conventional microphone units, as disclosed in the patent documents 1 and 2, for example, there are microphone units of type that vibrate a diaphragm by means of a difference between sound pressures acting on both surfaces of the diaphragm to convert a sound signal into an electric signal. Hereinafter, this type of microphone unit is sometimes expressed as a differential microphone unit.
A differential microphone unit is able to demonstrate an excellent distant noise alleviation performance in a case where it is used as a close-talking mike. Because of this, in usage of a mobile phone apparatus and the like which require the function of a close-talking mike, a differential microphone unit is useful.